Rosacea-like demodicidosis

Abstract

A 64-year-old woman presented with multiple asymptomatic, erythematosus papulopustular facial lesions (fi gure, A). The patient had been diagnosed with rosacea, and received oral doxycycline, 100 mg twice daily for 3 weeks as fi rst-line therapy by her family doctor. Because of the poor response to therapy, she had been referred to our dermatology clinic for further evaluation. On clinical examination, the eruptions, which were practically asymptomatic, had a rosacea-like appearance. They had emerged and gradually worsened over a period of 5 weeks. There were no pathological fi ndings on physical examination and routine laboratory test results were normal. Microscopic examination of specimens collected from the patient’s skin by epidermal scraping showed many Demodex folliculorum mites (fi gure, B, magnifi cation ×100). The patient showed substantial improvement after treatment with oral metronidazole (250 mg three times daily for 2 weeks) and subsequent weekly topical permethrin (cream 5%). Demodex spp are common saprophytic vermiform mites, which asymptomatically parasitise the hair follicles and the pilosebaceous glands of mammals. In human beings, two species of acarid mite have been identifi ed: Demodex folliculorum and Demodex brevis. Sites favoured by Demodex spp mites include the scalp, forehead, and chin, and areas around the orbit, nose, and mouth. Demodex spp have been implicated in the development of various facial conditions, including pityriasis folliculorum, rosacea-like demodicidosis (also known as demodicosis), pustular folliculitis, demodectic blepharitis, and so-called “demodicidosis gravis”. Clinical features of Demodex spp infestation include erythematopapulous and pustulous skin lesions together with erythematodesquamative changes of the face. Furthermore, demodicidosis should also be considered in any patient with rosacea-like dermatitis resistant to conventional rosacea therapies. Although there is no consensus to how and what degree infestation with Demodex spp mites contributes to skin pathology, there is evidence that demodicidosis is a condition distinct from common rosacea. The prevalence of Demodex spp carriers increases with age. It is possible that large numbers of demodex mites can stimulate infl ammatory or allergic reactions by mechanical blockage of follicles, or by acting as vectors for microorganisms, which ultimately results in connective tissue damage and telangiectasia. Another interesting hypothesis is that infl ammatory response may be stimulated by antigenic proteins related to a bacterium (Bacillus oleronius) isolated from D folliculorum.